Tuesday, November 27, 2012

New paper finds Roman Warming Period in Florida was warmer than today

A new paper published in Quaternary International reconstructs temperatures in SW Florida and finds that summer temperatures during the Roman Warm Period [RWP] from 300 BC-550 AD were "insignificantly different from today" and that winters during the RWP were "colder than today at 150-200 AD and 250-300 AD, similar to today at 200-250 AD, 300-350 AD and 450-500 AD, and warmer than today at 500-550 AD." The paper adds to hundreds of other peer-reviewed papers demonstrating temperatures during the Medieval, Roman, Minoan, and other unnamed warming periods were as warm or warmer than today.

The paper also shows that tiny variations in Total Solar Irradiance [TSI] of less than 1 W/m2 correlated with significant changes in reconstructed temperature of up to 5C. The IPCC claims that changes in TSI during the 20th century of about 1.5 W/m2 cannot account for 0.7C observed global warming, but data from this paper and others suggests otherwise. In addition, the paper shows TSI lagged by 50 years is better correlated to reconstructed temperatures, perhaps as a result of the enormous thermal inertia of the oceans. 
Modern temperature shown by double arrows on left vertical axis, coldest winter temps from 8 otoliths shown by red boxes. Grey line is variation in total solar irradiance [TSI] and black line is TSI lagged 50 years.
 Figure 6. Reconstructed Roman Warm Period and Vandal Minimum summers and winters in comparison with solar irradiance change. Symbols in red represent the Roman Warm Period and symbols in blue represent the Vandal Minimum. The thin line represents the variation of total solar irradiance ΔTSI (TSI value relative to the solar minimum 1365.57 Wm−2 in 1986) and the thick line represents the same profile as the thin line but with 50-year time lag (from Steinhilber et al., 2009). (B) Open circles represent coldest temperatures selected for evaluating winter temperature. Each open square represents each archaeological otolith specimen. The height of open squares represents its average winter temperature with standard error and the width of open squares represents its chronostratigraphic range. Double arrow represents the average winter temperature of modern otolith MOD2002 (from Wang et al., 2011).

Seasonal climate change across the Roman Warm Period/Vandal Minimum transition using isotope sclerochronology in archaeological shells and otoliths, southwest Florida, USA

  • a Department of Geological Sciences, University of North Carolina at Chapel Hill, Mitchell Hall, Campus Box # 3315, Chapel Hill, NC 27599, USA
  • b Florida Museum of Natural History, University of Florida, PO Box 117800, Gainesville, FL 32611-7800, USA

Archaeological evidence suggests that southwest Florida experienced variably warmer and wetter climate during the Roman Warm Period (RWP; 300 BC-550 AD) relative to the Vandal Minimum (VM; 550-800 AD). This hypothesis was tested by reconstructing seasonal-scale climate conditions for the latter part of the RWP (1-550 AD) by using high-resolution oxygen isotope ratios (δ18O) of archaeological shells (Mercenaria campechiensis) and otoliths (Ariopsis felis). Eight shells radiocarbon-dated to 150-550 AD recorded that the RWP summers at 150-250 AD were insignificantly different from today and the RWP summers at 250-350 AD and 450-550 AD were drier relative to today. Eight otoliths indicate that the winters were variable during the RWP, colder than today at 150-200 AD and 250-300 AD, similar to today at 200-250 AD, 300-350 AD and 450-500 AD, and warmer than today at 500-550 AD. The climate reconstructions agree with archaeological observations and are partially coherent with the history of sea-level change, with a drying and cooling trend at the 95% confidence level across the RWP/VM transition. The climate transition is not only consistent with falling sea level, but also coherent with reduced solar radiation. Reduced solar radiation may have triggered a change in atmospheric circulation patterns that precipitated the observed climate transition.

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